1. Field of the Invention
The present invention relates to a method for preparing a ceramic membrane for use in the separation of a condensible component.
2. Description of the Prior Art
In order to utilize, for the separation of a condensed component, a porous diaphragm with ultrafine pores having an average pore diameter of 10 to hundreds .ANG. which has been formed by sintering a metallic powder or a ceramic power or by compression-molding a powder of an organic synthetic resin such as a fluorine-contained resin, it is desirable that the porous diaphragm is molded into an optional shape, but in fact, such an optional molding is difficult. For this reason, for example, the following methods is taken in many cases: The thin porous diaphragm having the ultrafine pores is reinforced by the use of a porous material, which is high in a gas permeability, having a moderate thickness or by the use of a wire net so as to form a multi-layer structure and to thereby provide the diaphragm with an enough strength.
For example, for the purpose of molding the porous membrane having the multi-layer structure into a pipe shape, there are various methods. In general, the sheet-like multi-layer porous diaphragm is molded into a cylindrical shape, and butt welding or lap welding are then carried out at the edges of the diaphragm. However, the molding of the ceramic into the cylindrical shape is extremely difficult, because the ceramic is unflexible in contrast to a metal or the like. Further, with regard to a porous metal, its strength is lower due to being porous, i.e., owing to the existence of the pores therein, as compared with a nonporous material, in spite of the porous metal being within the category of the metal. Therefore, in the porous metal, a curvature radius within which its molding into the cylindrical shape is possible is limited, and it :s noticeably hard to mold it into a thin pipe.
Thus, as a means to solve such a difficulty, a process of molding the porous pipe is known which comprises concentrically disposing a pipe or a core metal inside or outside a porous supporting pipe, jetting a gas into a space portion between the porous supporting pipe and the pipe or the core metal and filling the space portion with a powder uniformly, while vibration is given to the porous supporting pipe and the pipe or the core metal, and compresively joining the filled powder in the space portion to the porous supporting pipe by means of static pressure molding in order to form the compresively joined layer of the powder on the porous supporting pipe (Japanese Patent Provisional Publication No. 77410/1975). In this method, however, the uniform filling of the powder and the preparation of the very thin membrane are poor, and in consequence, the above conventional method is difficult to practically perform.